1. Field of the Invention
This invention relates to an improvement in a cylinder block of an internal combustion engine, made of a light alloy.
2. Description of the Prior Art
In connection with automotive internal combustion engines, a cylinder block of the engine has conventionally been made of cast iron in order to obtain sufficient mechanical strength. However, such a cast iron-made cylinder block is heavy in weight and contrary to weight-lightening of the engine which is necessary particularly for the purpose of fuel economy. Accordingly, light alloy-made cylinder blocks, whose parent material is a light metal such as aluminium, have recently been employed.
Such a light alloy-made cylinder block is light in weight; however, it tends partially to be insufficient in mechanical strength, particularly, in main bearing bulkheads to which main bearing caps are installed. As a result, each bearing cap readily vibrates in forward and rearward directions thereof by which the bearing cap may come down. This vibration induces the vibration of a cylinder block skirt section which is integrally connected to the main bearing bulkheads, which vibration causes the skirt section to move inward and outward so as to flap. Furthermore, the vibration of the skirt section can be transmitted also to an oil pan which is securely connected to the cylinder block skirt section. Thus, considerable vibration noise is generated in and radiated from the cylinder block skirt section and the oil pan.